I have an M3ID which came with Octoprint installed on a Raspberry Pi. The Octoprint s/w has become damaged, it no longer functions correctly. Apparently this sometimes happens if an update gets corrupted somehow. I can no longer run the MakerGear Setup, it just hangs with "Loading", and I cannot enable SSH to get to the Pi and try to resolve it. For the normal OctoPi there is an SD card image download, but this does not have the customization for the M3ID. Where can I find an image that I can download so I can re-install the Pi?

You can download octopi image then install makergear plugin and it turns regular octoprint into makergear octoprint.
once you are up and running with octoprint go into plugin manager and install via url. Point to this https://github.com/MakerGear/MakerGear_ ... master.zip
after installation reboot the pi. I would switch the micro sd card so you can preserve the one that came with M3 and just load octopi on to new sd card